The majority of customers of the 'Big Six' energy companies are still missing out on savings of up to £400 a year, according to Which? research.

Ahead of the conclusion of the Competition and Markets Authority's (CMA) investigation into the energy market, Which? said the recent price cuts announced by the Big Six are dwarfed by the savings customers could be making by switching to an alternative provider.

Based on recently announced cuts, Which? claimed that customers on standard tariffs with the 'Big Six' providers would save just £30 a year - a 5% reduction for those on a standard single fuel gas tariff and only a 2.6% reduction for those on a standard dual fuel tariff, as the cuts only apply to gas, not electricity.

However, these same customers could save up to £400 a year if they were to switch to the cheapest dual fuel deal on the market, or £260 if they were on a gas-only tariff.

Government estimates only 12% of customers currently switch their gas provider. With seven in 10 (71%) gas customers stuck on standard tariffs and nine in 10 (88%) households still with the Big Six, Which? said the forthcoming energy inquiry must make it easier and engage significantly more people to switch to a better deal.

The research comes as Which?'s latest consumer tracker reveals 63% of people are worried about energy prices, while only a third of people (34%) trust energy providers.

Which? has submitted a dossier with a snapshot of stories from more than 30,000 customer comments to the CMA. The dossier details consumer dissatisfaction with energy companies and the market.

Richard Lloyd, Which? executive director, said: "Millions of people are still paying way over the odds for their energy and levels of switching, while increasing, are still woefully low. We would urge all consumers, especially those on a standard tariff with the Big Six, to switch to a cheaper deal today.

"The stakes are high for the outcome of the energy market investigation and consumers will be expecting action to protect the most vulnerable and bring about fairer energy prices."